1. Field of the Invention
The invention relates in general to new improved pulse modulators for converting analog information into a series of pulses.
2. Description of the Prior Art
Many communication channels utilize a modulator which converts analog information to pulses, for transmission to a remote location. The received pulses are demodulated to reconstruct the information into analog form. For example, the pilot protective relay apparatus disclosed in our application Ser. No. 084,218, filed Oct. 12, 1979, now U.S. Pat. No. 4,275,429, which is assigned to the same assignee as the present application, discloses protective relaying apparatus which, in a preferred embodiment, uses pulse period modulation (PPM). In addition to the usual advantages inherent in pulse communication, such as accuracy and reliability, PPM simplifies the demodulator due to the minimal filtering requirements.
While suitable modems for providing the desired modulating function are commercially available, it would be desirable to provide a new and improved pulse modulator which may be easily manufactured for a relatively low cost, and which is free of the start-up and latch-up problems experienced by certain prior art pulse modulators. Also, it would be desirable to provide a versatile pulse modulator which offers application flexibility merely by the selection of certain modes for its input signals.